1. Field of the Invention
The present invention relates to a drain pump provided in, particularly, an air-conditioner.
2. Description of the Related Art
Moisture in the air is condensed and attached to a heat exchanger during a cooling operation of an indoor unit of an air-conditioner, and water droplets drop into a drain pan provided below the heat exchanger. A drain pump is provided in the indoor unit in order to drain away drain water stored in the drain pan. An example of the drain pump, there is a drain pump where an inlet is formed at a lower end portion of a housing, an outlet is formed at a side portion of the housing, a rotary impeller is rotatably provided in the housing, a motor is fixed to an upper opening of the housing with a cover interposed therebetween, and the rotary impeller is rotated by the motor. When the rotary impeller is rotated by the drive of the motor, the drain water stored in the drain pan is sucked from the lower end of the inlet, is pumped along an inner surface of the housing, and is discharged to the outside from the outlet of the housing.
As the related art of this kind of drain pump, there is a drain pump disclosed in Japanese Patent Application Laid-Open (JP-A) No. 09-68185. FIG. 22 is a front view showing the partial cross-section of the entire structure of a drain pump disclosed in JP-A No. 09-68185, and FIG. 23 shows a top view and a side view of a rotary impeller of the drain pump. The drain pump, which is denoted by reference numeral 1, includes a motor 10 and a pump body 30 mounted below the motor 10 by a bracket 20. The bracket 20 is formed integrally with a cover 32 that covers an upper opening of the housing 40, and the cover 32 is connected to the housing 40 with a seal member 34 interposed therebetween. The housing 40 is made of plastic. The housing includes a pipe-like inlet 42 opened to the lower side, a pump chamber 44 formed in the housing, and an outlet 46 opened to the side. A suction end portion 43 of the inlet 42 is formed by a tapered surface of which an inner diameter is decreased toward an opened end.
A rotary impeller 50, which is rotated by the output of the motor 10, is received in the pump chamber 44 of the housing 40. The rotary impeller 50 includes a shaft portion 52, a plurality of flat plate-like large-diameter blades 60 that extends from an outer peripheral portion of an upper portion of the shaft portion 52 in a radial direction, and a plurality of flat plate-like small-diameter blades 54 that is connected to lower edge portions of the respective large-diameter blades 60 and is received in the inlet 42. The shaft portion 52 protrudes toward the motor 10 through a through hole 36 formed at the center of the cover 32, and a drive shaft 12 of the motor 10 is inserted into and fixed to a hole 53 formed at the center of an upper end of the shaft portion 52. A circular deflector board 14 is mounted on an upper surface of the shaft portion 52, and the circular deflector board 14 prevents drain water, which is ejected through the through hole 36 of the cover 32, from being scattered toward the motor 10.
Lower edge portions of the large-diameter blades 60 are formed in a tapered shape, and the lower edge portions are connected to each other by a disk-shaped annular member 62 that includes an opening 63 at the center of a lower edge portion. The small-diameter blade 54 and the large-diameter blade 60 are made of a resin and formed integrally with each other, and are disposed below the large-diameter blade 60. An auxiliary blade 68 is provided between the large-diameter blades 60 and 60, which are adjacent to each other, and it can secure a head of the pump by the auxiliary blades 68 and the large-diameter blades 60.
The outer peripheral ends of the large-diameter blades 60 and the auxiliary blades 68 are connected to each other by a ring member 64. The position of an upper edge portion of the ring member 64 is lower than the positions of the upper edge portions of the large-diameter blades 60 and the auxiliary blades 68. Air bubbles, which are generated in liquid by the rotation of the large-diameter blades 60, smoothly flow to the outlet 46 by the ring member 64. Accordingly, the collision between the air bubbles and a bottom face 35 of the cover 32 is mitigated, so that noise is reduced. Further, return water, which returns to a pump chamber 44 of the housing 40 from the outlet 46, is generated when a drain pump 1 is stopped. However, the return water bumps against the ring member 64 and is gradually diffused due to the buffering of the ring member 64, so that noise caused by the return water is also reduced. Meanwhile, if the position of the upper edge portion of the ring member 64 is set to be above or the same as the positions of the upper edge portions of the large-diameter blades 60 and the auxiliary blades 68 according to pump capacity (a head to be used), it may be possible to reduce noise.
A lower end portion of the ring member 64 is connected to an annular member 62, which connects the lower edge portions of the auxiliary blades 68 and the large-diameter blades 60, in an annular shape. The surface of drain water supplied upward from the inlet 42 is divided substantially in a vertical direction by the annular member 62, so that the amount of water coming into contact with the large-diameter blades 60 is decreased and the generation of air bubbles is suppressed. The inner peripheral portion of the annular member 62 has an opening 63 between the shaft portion 52 and itself. The lower edge portions of the auxiliary blades 68 and the large-diameter blades 60 are formed to be inclined toward small-diameter blades 64, and the annular member 62 is also formed in the shape of a dish so as to correspond to the inclination of the lower edge portions.
This kind of drain pump is also disclosed in, for example, JP-A Nos. 2004-138075 and 2007-127078 filed by the present applicant.
When power is supplied to an air-conditioner and the above-mentioned drain pump 1 begins to operate, drain water is splashed to the small-diameter blade 54, and torque is applied, so that suction begins and water is gradually introduced into the pump chamber 44. Water and air are mixed in the pump chamber 44 and gas-liquid mixture fluid collides with the rotary impeller 50. This collision causes vibration or noise of the scooping of water.
In the rotary impeller 50, many air bubbles generated at a gas-liquid boundary directly collide with the front surface of the large-diameter blade 60 and burst, and air bubbles are generated on the downstream side of the large-diameter blade 60. For this reason, cavitation noise and vibration are increased.
Further, when air bubbles, which are generated at the time of the start-up of the drain pump by the water scooping of the blade, collide with the inner wall of the housing and burst, cavitation noise is generated. The present applicant has proposed a drain pump that may reduce noise by modifying the shape of the inner portion of the upper edge portion of a cylindrical wall member of the rotary impeller in JP-A Nos. 09-68185, 2004-138075, and 2007-127078.
If the position of the upper edge portion of the ring member 64 is lower than the position of the upper edge portion of the large-diameter blade 60, it may be possible to reduce noise to some extent. However, the more efficient reduction of noise has not been particularly considered.